1. Field of the Invention
The invention relates to a rack bushing.
2. Description of the Related Art
Various rack bushings have been proposed which support a rack shaft in a housing so that the rack shaft is slidable in an axial direction (see, for example, Japanese Patent Application Publication No. 2008-126715 (JP 2008-126715 A) and Japanese Patent Application Publication No. 2009-286164 (JP 2009-286164 A)). In JP 2008-126715 A, the rack shaft is in surface contact with an area of an inner periphery of a cylindrical rack bushing. The area has an axial length approximately one third of the axial length of the rack bushing and includes an axially central portion of the rack bushing. In the rack bushing in JP 2009-286164 A, a recessed portion in which grease is stored is formed in a central portion of an inner periphery of a cylindrical main body in an axial direction. A pair of rack support portions shaped like cylindrical surfaces is provided such that the rack support portions are located at both sides of the recessed portion in the axial direction. The rack support portions are in surface contact with the rack shaft.
In JP 2008-126715 A and JP 2009-286164 A, the rack bushing (main body) is in surface contact with the rack shaft over a large area, resulting in increased sliding resistance of the rack shaft.